1. Field of the Invention
The present invention relates to a method and apparatus for securing a heat sink above a processor installed in a computer.
2. Description of the Related Art
Heat sinks are a vital part of any computer system. The heat generated by continued and extended use of a computer can severely damage the electrical components in the computer. Heat sinks provide a way for the heat to be transferred away from the source and away from critical components. To increase the amount of thermal transfer, heat sinks typically include a large surface area or a large number of thermally conductive fins. However, heavy heat sinks must be secured directly to the computer chassis in order to avoid transmitting inertial shock and vibration forces of the heat sink to the processor and the circuit board, possibility damaging the interface between the processor and the circuit board.
The contact area and pressure between the heat sink and the electrical components are also important considerations in heat sink design. A heat sink with a flat contact area is preferred since a thinner layer of thermal compound may be used. This reduces the thermal resistance between the heat sink and the heat source. The pressure between the heat sink and the heat source is typically high in order to maintain the requisite thermal contact and to facilitate thermal flow. Simple mechanical clips may help maintain the requisite pressure between the surface of the heat sink and the processor, but such clips are usually difficult to install and are not reliable when the computer is being shipped. Jarring that can occur during shipping or computer operation has the potential to cause disengagement of the electrical contacts between the processor and it's socket, causing the system to crash or significant contact damage.
The recent proliferation of Land Grid Array (LGA) sockets have created another problem that must be considered during heat sink design and particularly in the manner in which heat sinks or other cooling devices are attached to the socket/processor assembly. Current LGA socket designs frequently contain heat sinks as part of the assembly. The heat sink base is usually used as one of the loading plates in the assembly and is typically attached to a back-side stiffener using multiple screws or spring-loaded threaded fasteners.
Unfortunately, heat sinks may also transfer shock and vibration to the processor causing damage to the processor/socket interface. Physical shock may occur when a computer chassis is handled abruptly or dropped. Vibration may be caused by various components, such as a fan motor mounted to or adjacent to the heat sink. However, it is desirable to avoid transmitting physical shock and vibration to the processor. Consequently, the heat sinks may be supported by a shock absorber to reduce shock and vibration between the heat sink and the circuit board.
Aside from shock and vibration, the heat sink should be secured to the processor with a certain hold down force in order to maintain contact and high thermal communication between the processor and the heat sink. In fact, the hold down force may also be responsible for maintaining contact between the processor and a land grid array below the processor. For these reasons, it is desirable to connect the heat sink in a manner that provides a desired hold-down force but limits any ‘bounce’ or upward movement lessening the clamping force or breaking electrical contact.
Therefore, there is a need for an apparatus that secured a heat sink to a processor and to precisely deliver a desired hold-down force. It would be desirable to have a heat sink restraint assembly that was easy to use. It would also be desirable to have a heat sink restraint that was able to provide a range of desired hold-down forces and could be used with processors having a range of heights. It would be even further desirable if the heat sink restraint provided a visual indicator of the hold-down force that was being applied.